#!/usr/bin/env node

const log = console.log,
      arg = process.argv[2];

if(typeof(arg) === 'undefined' || arg === '--help' || arg === '-h') {
  help();
} else {
  calc();
}

function help() {
  const msg = ''  + 'usage: cmd-name [OPTION] [expression]\n'
                   + 'evaluate the expression.\n'
                   + '\n'
                   + 'Mandatory arguments to long options are mandatory for short options too.\n'
                   + '  -h, --help output help information and exit\n';
  log(msg);
}

function calc() {
  try {
    log(`${arg} = ${eval(arg)}`);      
  } catch(e) {
    console.error(`${arg} 不是合法的数学表达式！`);      
  }
}
